ACTIONS OF THE ANESTHETIC SAFFAN ON RAT SYMPATHETIC PREGANGLIONIC NEURONS IN-VITRO

1 Whole-cell patch-clamp recordings were used to investigate the effec ts of the anaesthetic Saffan on the electrophysiological properties of sympathetic preganglionic neurones (SPNs) in rat spinal cord slices. 2 Saffan (1-54 mu M) abolished or reduced the frequency of spontaneous action potential firing and abolished spontaneous, sub-threshold memb rane potential oscillations. Saffan caused dose-dependent decreases in input resistance and depending upon the initial resting membrane pote ntial, either a depolarization, a hyperpolarization or no change in me mbrane potential. 3 Responses ro Saffan were blocked by the GABA(A) re ceptor antagonists bicuculline (5-20 mu M) and picrotoxin (20 mu M), b ut not by the glycine receptor antagonist strychnine (20 mu M) indicat ing that they were mediated by GABA(A) receptors. 4 Changes in the pro perties of SPN action potentials were also observed. In the presence o f Saffan the amplitude and duration of the action potential after-hype rpolarization: were reduced and larger depolarizations were required i n order to evoke trains of action potentials. 5 To examine the effects of Saffan on electrotonic coupling between SPNs, experiments were per formed with the Na+ channel blocker QX-314 in the intracellular soluti on and antidromic oscillations were evoked by ventral root stimulation . Saffan failed to abolish antidromic oscillations, but reduced their amplitude and duration. This indicates that the abolition of spontaneo us membrane potential oscillations was not a direct effect on the coup ling between SPNs, but was a result of. the abolition of spontaneous a ctivity by Saffan. 6 The responses to Saffan occurred within the plasm a concentration range of Saffan during anaesthesia, suggesting that th e electrophysiological properties of SPNs may be altered during anaest hesia with Saffan. This would be expected to lead to changes in sympat hetic tone and in the integration of sympathetic output.